gcc@11 + CMake "cannot compile a simple test program"

[tcbrindle]

Like many others, I was recently bitten by the Github Actions changes, which broke Linux CI for my project.

Previously I installed GCC 11 via the straightforward brew install gcc@11 in my CI script. When brew went missing from my $PATH, I used the Homebrew/actions/setup-homebrew@master action to re-add it. This seems to work okay, in that brew install gcc@11 installs the compiler again, as requested.

Unfortunately I now have a another problem: when configuring CMake for my project with CXX=g++-11 I get an error as follows:

-- Configuring incomplete, errors occurred!
  The C++ compiler
See also "/home/runner/work/libflux/build/CMakeFiles/CMakeOutput.log".

See also "/home/runner/work/libflux/build/CMakeFiles/CMakeError.log".

    "/home/linuxbrew/.linuxbrew/bin/g++-11"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: /home/runner/work/libflux/build/CMakeFiles/CMakeTmp
    
    Run Build Command(s):/usr/bin/make -f Makefile cmTC_c0a0f/fast && /usr/bin/make  -f CMakeFiles/cmTC_c0a0f.dir/build.make CMakeFiles/cmTC_c0a0f.dir/build
    make[1]: Entering directory '/home/runner/work/libflux/build/CMakeFiles/CMakeTmp'
    Building CXX object CMakeFiles/cmTC_c0a0f.dir/testCXXCompiler.cxx.o
    /home/linuxbrew/.linuxbrew/bin/g++-11    -o CMakeFiles/cmTC_c0a0f.dir/testCXXCompiler.cxx.o -c /home/runner/work/libflux/build/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
    Linking CXX executable cmTC_c0a0f
    /usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_c0a0f.dir/link.txt --verbose=1
    /home/linuxbrew/.linuxbrew/bin/g++-11 -rdynamic CMakeFiles/cmTC_c0a0f.dir/testCXXCompiler.cxx.o -o cmTC_c0a0f 
    /usr/bin/ld: cannot find -lm

I'm not really sure what's going on -- why can Homebrew-installed GCC now suddenly not find system libs? All was working fine a few days ago!

The GH Actions logs can be found here, and my (revised) CI script is here. Please let me know if there are any more details which would be helpful :)

[carlocab]

Sorry, this was broken by recent changes that required making glibc keg-only. Homebrew/homebrew-core#111830 needs to be backported to gcc@11.

As a workaround in the meantime, please do

brew link --force glibc

CC @Homebrew/linux

[danielnachun]

I am going to backport the changes to all non-deprecated versions of GCC as they are trivial.

[danielnachun]

Homebrew/homebrew-core#112555

[danielnachun]

Homebrew/homebrew-core#112555 has been merged and should fix this. Please try to run your workflow again and let us know if it works.

[tcbrindle]

Thank you!

I have just re-run my troublesome job and this time it gets to the build stage before erroring out with

[  2%] Building CXX object test/CMakeFiles/catch-main.dir/catch_main.cpp.o
as: unrecognized option '--gdwarf-5'
make[2]: *** [test/CMakeFiles/catch-main.dir/build.make:76: test/CMakeFiles/catch-main.dir/catch_main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:100: test/CMakeFiles/catch-main.dir/all] Error 2
make: *** [Makefile:101: all] Error 2
Error: Process completed with exit code 2.

Log

I'm not sure where the --gdwarf-5 option is coming from, or why as doesn't like it.

[danielnachun]

You need to also have brewed binutils in your path, because the host binutils is too old. It is keg-only so you'll need something like PATH=$(brew --prefix)/opt/binutils/bin:$PATH in your path.

[danielnachun]

Or alternatively, brew link --force binutils.

[tcbrindle]

Thank you, this fixed it 👍

Are the binutils changes documented anywhere?